This concept of the current has had a fate typical of the whole
relation of human thought to the facts connected with electricity. Long
after it had been coined to cover phenomena which in themselves betray
no movement of any kind between the electrical poles, other phenomena
which do in fact show such movements became known through Crookes's
observations. Just as in the case of atomism, they seemed to prove the
validity of the preconceived idea of the current. Soon, however,
radiant electricity showed properties which contradicted the picture of
something flowing from one pole to the other. The cathode rays, for
instance, were found to shoot forth into space perpendicularly from the
surface of the cathode, without regard to the position of the anode. At
the same time Maxwell's hydrodynamic analogy (as our historical survey
has shown) led to a view of the nature of electricity by which this
very analogy was put out of court. By predicting certain properties of
electricity which come to the fore when its poles alternate rapidly, he
seemed to bring electricity into close kinship with light. Mathematical
treatment then made it necessary to regard the essential energy process
as occurring, not from one pole to the other, but at right angles to a
line joining the poles (Poynting's vector). This picture, however,
satisfactory though it was in the realm of high frequency, failed as a
means of describing so-called direct-current processes.

As a result of all this the theory of electricity has fallen apart into
several conceptual realms lying, as it were, alongside one another,
each consistent in itself but lacking any logical connexion with the
others. Although the old concept of the electric current has long lost
its validity, scientific thought (not to speak of the layman's) has not
managed to discard it. To do this must therefore be our first task, if
we want to attain to a realistic picture of electromagnetism.